It’s hard to picture the universe in its infancy. The middle-aged cosmos now stretches across 93 billion light-years, holding up to two trillion galaxies and more than 200 billion trillion stars. But in the beginning, things were simple. As a baby, the universe was essentially a hot, dense soup of particles, which has been expanding and cooling over billions of years. A telescope perched in northern Chile has peered back at the early universe, capturing the afterglow of the Big Bang that radiated throughout the cosmos.
The Atacama Cosmology Telescope (ACT) released the sharpest images yet of the universe’s first light, capturing the material that would later form the earliest galaxies and stars during the cosmic infancy. The new images, to be presented at an upcoming meeting of the American Physical Society, date back to when the universe was only 380,000 years old. The cosmos is now a more mature 13.8 billion years old, which means the light had to travel more than 13 billion years to reach the telescope.
“By looking back to that time when things were much simpler, we can piece together the story of how our universe evolved to the rich and complex place we find ourselves in today,” Jo Dunkley, physics and astrophysical sciences professor at Princeton University, and the ACT analysis leader, said in a statement.
This is the earliest cosmic time accessible to our viewing. That’s because light would frequently scatter off of free electrons, making the universe opaque. It wasn’t until 380,000 years after the Big Bang when particles began to combine, allowing light to travel freely and ending the cosmic dark ages.
The cooled remnant of the first light that permeated the universe is known as the cosmic microwave background—leftover radiation from the Big Bang that can still be detected in the distant universe. This ancient light carries with it clues to the universe’s past, as well as its future, allowing astronomers to get as close as possible to the Big Bang to be able to understand the birth and evolution of the cosmos.
After staring at the cosmic skies from a mountaintop in Chile for 15 years, ACT was able to measure the intensity and polarization of the universe’s first light with extreme sensitivity. This allowed scientists to estimate the temperature, density, and velocity of the swirling material that occupied the baby universe, gauging just how much of it was there before it began forming galaxies and stars.
The polarization of the material reveals the detailed movement of hydrogen and helium during cosmic infancy. “We are seeing the first steps towards making the earliest stars and galaxies,” Suzanne Staggs, director of ACT and professor of physics at Princeton University, said in a statement. “And we’re not just seeing light and dark, we’re seeing the polarization of light in high resolution…Like using tides to infer the presence of the moon, the movement tracked by the light’s polarization tells us how strong the pull of gravity was in different parts of space.”
The images are helping scientists gather clues to the universe’s origin story. By looking over ACT’s measurements, the team behind the research was able to confirm the age of the universe at 13.8 billion years old, with an uncertainty of only 0.1%. “A younger universe would have had to expand more quickly to reach its current size, and the images we measure would appear to be reaching us from closer by,” Mark Devlin, professor of astronomy at the University of Pennsylvania, and ACT’s deputy director, said in a statement.
The team was also able to measure more precisely that the universe extends out to about 50 billion light-years in all directions away from us, and contains as much mass as 1,900 zetta-suns, or the equivalent of almost two trillion trillion Suns.
Rather than coming up with new theories, the measurements confirm that it’s business as usual for our surrounding cosmos. “Our standard model of cosmology has just undergone its most stringent set of tests. The results are in and it looks very healthy,” David Spergel, professor of astronomy at Princeton University, said in a statement. “We have tested it for new physics in many different ways and don’t see evidence for any novelties.”
